Thermodynamics - Introduction

ME 302 - THERMODYNAMICS

Course Instructor

Engr. Uzair Khaleeq uz Zaman

Course Plan

Credit Hours = 2 1

Text Book

Fundamentals of Engineering Thermodynamics by Michael J. Moran and Howard N. Shapiro (5th or 7th Edition)

Reference Books

Thermodynamics: An Engineering Approach by Y. A. Cengel and M. A. Boles, Latest Edition

Applied Thermodynamics by T.D. Eastop and A. McConkey

Course Plan (contd)

Course Objectives & Learning Outcomes

Gain basic knowledge and skills in the area of thermodynamics

Understand the concept of heat energy, fluid properties, inter-conversion of heat and work, reversible and irreversible processes

Attain better understanding of operational procedure of machines such as IC Engines, Turbo machinery, Steam and Gas Turbines,

Compressors, etc.

Learn about inter-conversion of heat and work energies

Gain sufficient knowledge to understand power plant basics and operational / maintenance procedures for static and /or rotary

equipment

Understand the concepts which will help design thermal systems.

Course Plan (contd)

Lectures Schedule

Sr. No. Topic Week / Lecture

1

Introductory concepts and definitions, types of systems,

temperature and pressure scales, evaluating energy transfer by

work and heat, first law of thermodynamics, types of cycles and

respective calculations

1-3

2

Properties of a system; pressure-volume, pressure-volume

temperature and temperature-volume curves, phase change,

concepts of internal energy and enthalpy, gas laws and respective

calculations

4-5

3 Control Volume Analysis: Turbines, nozzles and diffusers,

compressors and pumps, heat exchangers, and throttling devices 6-8

4

The Second Law of Thermodynamics: Statements of the 2nd Law,

heat engines, refrigeration devices, reversible versus irreversible

processes, the Carnot cycle and respective calculations

9-11

5

Entropy and Enthalpy-Clausius inequality, the increase in entropy

principle, entropy change of pure substances, enthalpy and

specific heats;

12-13

6 Vapor Power Systems and Gas Power Systems 14-16

Course Plan (contd)

Grading System

Sessional = 25 %

Quizzes/Assignments = 10 %

Lab = 25%

Final Exam = 40 %

Introductory Concepts and Definitions

What is Thermodynamics? Storage

Transformation

Transfer

Storage in terms of

Internal energy (associated with temperature)

Kinetic energy (due to motion)

Potential energy (due to elevation)

Chemical energy (due to chemical composition)

Transformation from one form to another

Transfer across a system boundary as heat or work

ENERGY


(contd)

The word; Thermo-dynamic

First used by Thomson (later Lord Kelvin)

Has Greek origin

Translated as the combination of

Introductory

Concepts and Definitions

(contd)

Applications

Automobile Engines

Compressors, Pumps

Turbines

HVAC&R systems

Solar activated heating and

Power generation

Biomedical Applications

Life support systems

Cooling of Electronic

Equipment


(contd)

Plot KE(t) and PE(t) with and without drag forces, g = 9.81m/s2


(contd)

Functions of KE(t) and PE(t)

Without Drag force With Drag force

Same amount of PE but less KE Less Total Mechanical Energy = >

THERMAL ENERGY


(contd)

System

Whatever we want to study (quantity of fixed mass under investigation)

As simple as a free body

As complex as a refinery

Content inside the system may change or remain fixed by chemical reactions

Surroundings

Everything external to the system

System Boundary

Interface separating system and surroundings

May be at rest or in motion


(contd)

Heat can get into the system

(Potato can get hot)

Work can cross out of the system

(Potato can expand)


(contd)

Types of Systems

1. Closed System (Control Mass)

Contains fixed quantity of matter

Always contains the same matter

NO MASS TRANSFER ACROSS THE BOUNDARY

2. Open System (Control Volume)

Region of space through which mass can flow

MASS TRANSFER ACROSS BOUNDARY

3. Isolated System

NO INTERACTION WITH THE SURROUNDINGS

Potato with THICK and INELASTIC skin


(contd)

Control Surface

When the terms control mass and control volume are used, the boundary of a system is referred to as the control surface


(contd)

How to Select System Boundary

What is known about the system

Objective of the analysis

Example: Air Compressor and storage tank

System boundary encloses what?

If electrical power input is known,

this boundary might be selected.

Objective:

How long compressor must operate for

the pressure in the tank to rise to a

specified value?


(contd)

Macroscopic vs Microscopic

Macroscopic (Classical Thermodynamics)

Overall system is studied

No models of the structure of matter at molecular, atomic and sub atomic levels are used

Microscopic (Statistical Thermodynamics)

Concerned directly with the structure of the matter

Average behavior of particles making up a system is studied


(contd)

Continuum (Assumption of matter in this course) Discrete changes from molecule to molecule can be ignored

Distances and times are much larger than those of the molecular scale (continuously distributed through out region of interest)

Applications of continuum assumption

Rarefied gas dynamics of outer atmosphere (for low orbit space vehicles)

Nano-scale heat transfer (in cooling of computer chips)

ENABLE THE USE OF CALCULUS IN CONTINUUM

THERMODYNAMICS


(contd)

Properties and State of a Substance Phase

Quantity of matter that is homogenous throughout In chemical composition In physical structure

Phase Boundaries Interfaces between different phases

Pure Substance Uniform and invariable in chemical composition Can exist in more than one phase BUT chemical composition must be

the same in each phase

If one phase is not identical to other phase = NOT a pure substance

Example of single phase ICE, LIQUID WATER

Example of two or multi phase mixture GLASS OF ICE WATER Phase boundaries = at the edge of each ice cube


(contd)

Properties and State of a Substance (contd)

State

Condition described by observable macroscopic properties

Property

Macroscopic characteristic, has a unique value

Quantity that only depends on the state of the system and is independent of the history of the system

Ex: Mass, Volume, Temperature, Pressure, Energy

TWO STATES ARE EQUIVALENT IF THEY HAVE THE SAME PROPERTIES = NOTE


(contd)

Properties and State of a Substance (contd) Process

Transformation from one state to another

When property changes, state changes, and process occurs

Steady State

When properties remain same, state remains same

None of the properties change with time

Thermodynamics Cycle

Sequence of processes that begins and ends at the same state

Change in value of a property from one state to another is solely dependent on the two end states and is INDEPENDENT of the path of the process


(contd)


Extensive Property

Depends on the mass (or extent) of the system

Its value for an overall system is the sum of its values for parts into which it is divided

Can change with time

Ex: mass, total volume, total energy

Intensive Property

Independent of the mass of the system

Ex: Temperature, Pressure, Specific Volume

What would happen

to the extensive and

intensive properties

when you cut a

system in half?


(contd)


Equilibrium

Condition of balance / No spontaneous changes observed with respect to time

Procedure to attain equilibrium

ACTUALLY WE NEVER REACH EQUILIBRIUM, WE ONLY APPROXIMATE IT (It takes infinite time to

reach final equilibrium)

ISOLATE SYSTEM FROM

SURROUNDINGS

WATCH ANY CHANGE IN PROPERTIES

IF NO CHANGE, AT EQUILIBRIUM


(contd)


Equilibrium (contd)

Mechanical Equilibrium = Characterized by Equal Pressure

Thermal Equilibrium = Characterized by Equal Temperature

Metastable Equilibrium = If a system would undergo large change in its properties when subjected to small disturbance

(Ex: mixture of gasoline and air or large bowl on a small table)

PROCESS vs QUASIEQUILIBRIUM PROCESS ??


(contd)


Quasiequilibrium Process

Process in which the departure from thermodynamic equilibrium is almost not possible (infinitesimal)

Each state can be considered as equilibrium states

Why do we want to model a process as quasiequilibrium?

To develop systems which can give qualitative information

To deduce relationships that exist among propoerties at equilibrium

Helps to generate constant line on P-V diagram


(contd)


Quasiequilibrium Process (contd)

Thermodynamically slow

compression of air in a

cylinder = Quasiequilibrium

process

Combustion in a cylinder = series

of non-equilibrium states

Dashed because properties are not

uniform = State cant be defined

Solid because properties are

uniform = State can be defined


(contd)


Quasiequilibrium Process (contd)

If I need to add weight, W, on a piston, how should I add it in:

Quasiequilibrium manner?

Non-equilibrium manner?

Cycle

When a system in its initial state experiences a series of quasiequilibrium processes and returns to the initial state,

the system undergoes a cycle.


(contd)

Fundamental Variables and Units

Mass

Kilogram (kg) = a mass equal to the mass of the international prototype of the kilogram (a platinum

iridium bar stored in Paris), roughly equal to the mass of

one litre of water at S.T.P

Pound mass (lbm)

Length

Meter (m) = length of the path travelled by light in vacuum during a time interval of 1/299792458 of a

second

Foot (ft)


(contd)

Fundamental Variables and Units (contd)

Time

Second (s) = the duration of 9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom

Second (s) = English time unit identical to SI unit

Temperature

Kelvin (K)

Celsius (oC)

Rankine (oR)

Fahrenheit (oF)

Introductory Concepts and

Definitions (contd)

Secondary

Variables and

Units

Force

Energy

Specific

Volume

Density

Pressure


(contd)

Measurable Properties

Density

Depends on relativity of continuum

Intensive property

May vary from point to point in the system

Specific Volume

Inverse of density (volume per unit mass)

Intensive property (may vary from point to point)


(contd)

Measurable Properties (contd)

Molar Basis

To express sp. Volume on molar basis in terms of kmol or lbmol (used in certain applications)

Ratio of mass (kg) and molecular weight (kg/mol)

Documents

Thermodynamics - Introduction